If someone did that to my car, and then tried to evade responsibility, and then tried to give me some BS about "needing a valve job soon anyway," I would judge them to be both incompetent and dishonest. I would not trust them to go any further.
IMHO, you should get your car out of there ASAP, and to a competent shop - R & H in Owings Mills comes to mind. There are several other good shops.
Then you need to see a lawyer about damages.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe